(1) Field of the Invention
This invention relates to a method and apparatus for the focal form cutting of a preferably moving web of material by means of a laser beam.
(2) Description of the Prior Art
The form cutting of paper, cardboard, or the like is generally effected by a blade or a set of blades. Blades and sets of blades require a cutting device which holds them and guides them during the cutting movement. The cutting device, necessarily mechanical, and the blades or sets of blades are subject to wear, are relatively complicated and costly, and allow only a limited cutting speed as well as, in the case of periodic operation, only a limited cutting frequency.
To avoid the disadvantages of mechanical blades it is already known to have a cut effected by the focal spot of a laser beam. To make a two-dimensional cut, moreover, suggestions have already been made for deflecting the laser beam at its cutting point one-dimensionally on one or more straight cutting paths which run obliquely or transversely to the direction of movement of the material, at controlled speeds. If a rectangular blank is to be cut by this process from a moving material web, commencing at the edge as shown in FIG. 1a, then the laser beam must first be deflected inwardly on a straight path which runs oblique to the direction of movement, and then it must be deflected outwardly on a second straight path which also runs oblique to the direction of movement of the material. The two cutting paths form an isosceles triangle on the material web as shown by broken lines 1, 2 in FIG. 1a. The speed of movement of the laser beam over the web is a function of the direction of movement and the speed of feeding of the web. The movements are oscillatory and, to obtain such directions of movement of the laser beam according to the prior art, relatively complicated mirror-deflection devices consisting of several elements are necessary. Particular difficulties arise regarding the focussing of the laser beam on the web since the distance between the web and the collector lens, i.e. the focal length, alters as a result of differing angles of deflection.